Fibrous catalyst structures for oven walls

ABSTRACT

This invention relates to paper-like catalytic structures which are applied to oven walls to render them self-cleaning. These structures are comprised of a catalytic material uniformly distributed throughout a porous fibrous support material.

United States Patent 1 1 Stiles June 12 1973 FIBROUS CATALYST STRUCTURES FOR OVEN WALLS [56] References Cited [76] Inventor: Alvin B. Stiles, 1301 Grayson Road, UNITED STATES PATENTS Welshire, Wilmington, Del. 19810 3,159,156 12/1964 lncledon 126/19 [22] Filed: May 1972 Primary Examiner-Edward G. Favors [21] App]. No.: 252,769 Attorney-Lynn N. Fisher [60] Related U.S. Application Data [57] ABSTRACT Division of Ser. No. 46,550, June 15, 1970, which is a continuationdmpart of Set No. 803,560 March 3 T218 illnventlon relates to paper llike catalytic structures 1969 abandoned w 1c are applied to oven wa ls to render them selfcleaning. These structures are comprised of a catalytic [52] U 8 Cl 126/H9 R 26/273 l26/39 M material uniformly distributed throughout a porous fi- 51 Int. Cl A211: 1/00 bmus SuPPort matenal- [58] Field of Search 126/19, 273, 39 M 5 Claims, No Drawings FIBROUS CATALYST STRUCTURES FOR OVEN WALLS CROSS-REFERENCE TO RELATED APPLICATIONS This application is a divisional of my copending application Ser. No. 46,550, filed June 15, 1970, which application is a continuation-in-part of my then copending application Ser. No. 803,560, filed Mar. 3, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the application of paperlike fibrous catalytic structure on the interior surfaces of an oven cavity to produce an oven capable of oxidizing at normal operating temperatures, waste material generated during use.

As is well known, the difficulties experienced in cleaning cooking devices have led to the development of a pyrolytic self-cleaning oven. The pyrolytic oven operates by burning out food residues at temperatures in the neighborhood of 800 to 900 F. This method thus has the disadvantage of requiring high temperatures for cleaning. As described in US. Pat. No. 3,266,477, a method for cleaning cooking devices at lower temperatures by oxidation and without abrasion has been discovered. Thus at moderate temperatures of say 400 to 500 F. or even lower in some cases, cooking devices can be cleaned without overheating a kitchen or work area and without other attendant difficulties of high temperatures such as distortion of equipment and requirements for large amounts of insulation.

A particularly vexing problem in the operation of cooking devices is that of dealing with massive cooking spills. A massive cooking spill is understood as relating to a spill resulting from boiling over and the like, rather than the ordinary splattering that occurs during the cooking process. This invention is directed to a product that efficiently eliminates such unsightly massive spills.

SUMMARY OFTI-IE INVENTION I have discovered that the application of paper-like fibrous structures containing oxidation catalysts to the interior surfaces of an oven cavity produces an oven capable of oxidizing at normal operating temperatures, waste material generated during use.

It will be understood that conventionally impregnated catalytic mats can be applied to interior oven surfaces as well as the improved catalytic structures made by the process of my application Ser. No. 46,550, filed June 15, 1970, the disclosures of which are incorporated herein by reference.

DESCRIPTION OF THE INVENTION This invention relates to formed paper-like structures which are attached to oven walls and are useful in absorbing or otherwise trapping waste materials and oxidizing said materials at low temperatures but are also stable up to 1,000 F. or even above. The structures can also be placed without attachment on the bottom or floor of an oven to absorb and oxidize drippings and the like.

The structures are comprised of a non-combustible, fibrous support material and a catalytic material. In addition, the structures can also contain a cementing material and a filler.

Typical of the fibrous support materials employed in preparing the structures are glass wool, rock wool, fibrous ceramic alumina, quartz fibers, refractory metallic filaments, zirconia fibers, sillimanite fibers and asbestos fibers.

The catalytic component of the structures are those oxidizing agents effective at low temperatures but also stable up to temperatures of about 1,000 F. or even above. Such catalysts are known in the art for use in the complete oxidation of hydrocarbons, oils, greases, esters, organic acids, aldehydes, ketones and other organic materials.

The cement or binder component of the compositions of this invention are well known to the art and include materials such as calcium aluminate, magnesia cement, anhydrous calcium sulfate (plaster of Paris) portland cement, hydraulic cement and colloidal silica. Of the above calcium aluminate is the preferred cement.

It will also be understood that certain catalysts or their precursor salts can act as the cement in the structures.

A filler material can also be employed to give body and rigidity to the catalytic structures resulting in a product having a higher degree of structural integrity than generally found in fibrous paper-like mats. The filler can be a non-fibrous material which may or may not be catalytic. Representative of the fillers that can be employed are kieselguhr, diaspore, alumina, bauxite, aluminum hydroxide, magnesium hydroxide, magnesia, bentonite and montmorillonite. In some instances the filler can additionally act as the cement especially in the case of clays such as the bentonite or montmorillonite.

In addition to the above listed ingredients of the compositions of this invention, pigments can also be employed in the preparation of said compositions to improve the aesthetic properties of the finished product.

In some instances the catalytic material employed will provide such pigmentation. For example, cobalt aluminate will lend a blue color to the finished product, nickel aluminate will lend a green color to the finished product and platinum metal will result in a white product when the other component parts of the finished product are selected to provide a white finished product.

The useful catalytic structures can be made by conventional techniques, e.g., the catalyst is incorporated in non-combustible fiber supports, such as wool-like asbestos mats, by impregnation. In this embodiment the fiber supports are made by any of the conventional techniques. The fiber supports are then treated with solutions which upon drying and if necessary calcining, provide an oxidation catalyst on the fibers. The useful oxidation catalysts or their precursors are set forth hereinafter.

In a preferred embodiment the structure is prepared by incorporating the catalytic material in a paper beater mix prior to compression and drying into the paperlike structure. Incorporating the catalyst into the beater mix enables some of the catalysts employed to bond with the surface of the fibrous support material as the result of natural attractive forces in a fluid system. Therefore, in addition to a product in which the catalyst is more uniformly distributed throughout the support material, better adhesion of the catalyst to the surface of the support fibers is achieved. Details on preparing such catalysts and their physical properties can be found in application Ser. No. 46,550, filed June 15, 1970.

In general in making such preferred structures, the fibrous support material is incorporated into a dispersion medium such as water or suitable organic solvent and a slurry is formed by mechanical agitation. The slurry thus formed will contain from 0.2 to percent solids and preferably will contain from 2 to 8 percent solids. The dispersion medium can be water or an organic liquid such as methanol, acetone or carbon tetrachloride.

The dispersion medium chosen must be compatible with each of the various components of the finished product.

As stated above, the slurry, also called the beater mix, is agitated until a homogeneous mixture is obtained. The beating time is controlled to insure that the fibrous support material becomes dispersed into its ultimate fibrils. For this purpose commercially available paper making machinery such as the hollander-type beater, jordan refiner, Claflin refiner, l-lydrafiner and the like can be employed.

Catalytic material as well as the cement, fillers and other components are added to the beater mix near the end of the homogenization.

The catalytic material can be a catalyst per se, a catalyst precursor or a catalyst supported on an insert refractory such as alumina, alumina-silica, bauxite, pumice and the like. Such catalytic material will be added to the beatermix as a solid, in solution, or as a suspension. When added as a solid or as a suspension, the catalytic material will be in the form of finely divided particles, preferably ofa size which will pass through a 325 mesh screen. There is actually no lower limit on the particle size of the solid catalytic material, but as a practical matter, the material will generally be larger than about 600 mesh since smaller particles are not readily obtained in substantial quantities by the ordinary methods of mechanical subdivision used in mak ing catalysts.

The catalytic materials as noted above can be any of the solid inorganic compounds commonly used as oxidation catalysts. Thus there can be used the oxides, cerates, chromates, chromites, manganates, manganites, molybdates, tungstates and vanadates of such metals as iron, cobalt, nickel, palladium, platinum, ruthenium, rhodium, manganese, chromium, copper, molybdenum, tungsten, and the rare earths, including lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thullium, ytterbium, and lutetium, or their mixtures. The precious metals such as ruthenium, rhodium, palladium and platinum can of course also be used in the oxide or elemental form. Solid compounds of the catalytic metals which decompose upon heating to provide the oxides can of course also be used. These include the hydroxides, carbonates, nitrates, and organic salts of the various metals.

Preferred catalysts because of their comparatively high activity at low temperatures are ruthenium, palladium, and platinum metals and the oxides, cerates, manganates, or manganites, chromates or chromites or vanadates of cobalt, nickel, cerium, manganese, ruthenium, palladium, platinum and the rare earths. Also preferred are the mangano-chromia-manganite cata' lysts disclosed in Howk and Stiles U.S. Pat. No. 3,216,954.

The cement can include compounds such as calcium aluminate magnesia cement, portland cement, hydraulic cement, anhydrous calcium sulfate, colloidal silica and the like. The catalyst itself or its precursor, such as the nitrate salts of the catalytic metals can be employed as the cement.

After the catalyst and other materials are added to the beater-mix, agitation is continued until a homogeneous mixture is obtained.

The homogeneous beater-mix can then be formed into a continuous sheet using standard papermaking equipment such as the cylinder machine or the Fourdrinier.

The catalytic mat formed as described abovecan be used as such in various applications or can be further treated by embossing, printing with appropriate designs or by formation into rigid structures, as described.

The compositions of this invention when formed into rigid sheets are well suited for use in the bottom of household cook stoves to completely oxidize oils, greases and organic spillovers from normal cooking operations. The sheet, of course, should be thick and porous enough to absorb and distribute the spills while oxidation is taking place without blinding the catalytic material. Generally the formed catalytic sheets will be from 0.005 to 0.125 inch in thickness.

Such sheet compositions of this invention can be attached mechanically by means of adhesives or clamps to the walls, top, bottom or door of ovens to constitute an easily replaceable oxidation catalytic structure. Of course, if desired, the sheet can merely be placed on the bottom of an oven and no attachment is necessary. Such a porous catalyst structure has the advantage over known structures of providing a catalytic structure in which the catalyst is uniformly distributed and further, which permits air diffusion from all directions and which minimizes the blinding of the catalyst when said structure is subjected to heavy soils resulting, for example, from food spills.

It will be understood that the term oven as employed herein is used in its generic sense to identify a chamber which is heated by a heating means and employed for baking, heating or drying. Specifically, this term is intended to include home cooking ovens, commercial cooking ovens, paint drying ovens and the like.

The paper-like fibrous catalytic structures can be applied to the interior surfaces of the oven by any suitable fastening means. It will be understood that the fastening means include devices such as screws, snaps, clips and the like; or a heat stable adhesive material such as potassium, lithium or sodium silicate, ethyl silicate, guanidine silicate, colloidal silica, aluminum hydroxide gel and magnesium hydroxide gel. It will be understood that the adhesive is not intended to be limited to those enumerated above and that any adhesive material suitable for bonding the paper-like fibrous catalytic structure to the interior oven surfaces which is stable within the normal temperature range of the oven can be employed.

It will be understood that the adhesive material can be applied to the interior surfaces of the oven and the catalytic structure can then be applied. Alternatively the adhesive material can be applied to the catalytic structure or to both the oven surface to be altered and the catalytic structure as desired.

The following examples are presented to further illustrate the products and processes of this invention.

EXAMPLE I l. A woven asbestos cloth having a twill weave and a thickness of approximately one-sixteenth inch was impregnated as a 24 X 24 inch sheet by immersing in an aqueous solution comprising 5 percent nickel nitrate hexahydrate, 5 percent manganese nitrate hexahydrate and 5 percent chromium nitrate nonahydrate.

2. The wet asbestos sheeting was dried and then calcined to deposit a mixture of finely divided nickel, manganese and chromium oxides.

3. The sheet was cut into suitably sized strips and each strip was coated on one side with a solution of ethyl silicate.

4. While still moist the sheet was applied to a domestic oven wall and Items 13 were repeated until all walls, back, front and bottom, of the oven had been completely coated.

5. The coating thus produced provided an effective catalytic surface to oxidize soils derived during cooking.

Similarly applied walls on industrial ovens such as those used to bake asphalt impregnated asbestos or ceramic fibers were thus converted to surfaces which would oxidize odorous combustible products from the drying and baking operation. When such ovens are used also for baking plastic articles, a similar abatement of fumes and odorous materials is achieved.

Instead of the asbestos cloth specified in Item 1, there can be used other woven fabrics such as spun bonded or woven glass fabrics, silica fabrics, carbofrax fabrics or even Teflon or other organic or halo-organic fabrics if the temperature is not excessive to cause melting or heat deterioration.

Instead of the catalytic materials specified in Item 2 above, there can be used other catalytic materials known in the art and instead of using the catalytic materials as the nitrate, other salts such as acetate, oxalate, carbonate, amminenitrate, amminecarbonate can also be used. In some cases an especially effective catalyst can be made from the alkaline chromate or the soluble chromate salts of copper, nickel, cobalt, for example.

EXAMPLE 2 l.Ten parts by weight ofa v; X 7% X A: stoichiometric mixture of cobalt oxide, manganese oxide and cerium oxide is prepared as a finely divided powder passing 100 percent through a 325 mesh screen. This mixed oxide plus 10 parts by weight of fine denier silica fibers as A inch chopped fibers and 1 part by weight of colloidal alumina are slurried together with 400 parts by weight of water to form a beater mix.

2. After 25 minutes of agitation in the beater, the uniform slurry was processed through a typical papermaking machine on the filter screen of which was placed a sheet of woven net with ,4; inch openings and fabricated from silica fibers. This was processed in such a way as to produce a sheet with the woven net of silica fibers as a reinforcing member.

3. The sheet thus produced was dried and then onehalf was further calcined at 800 C. to cause a coalescing and strengthening of the fiber composite.

4. The sheet was divided into 4 inch wide X 18 inch long strips and were each coated on one side with sodium silicate solution.

5. The strips were then applied directly to the walls of a domestic cookstove oven and were allowed to dry thereon. One wall was coated with the sheet which had been simply dried at C., whereas another wall was coated with the more rigid sheet which had been heated to 800 C.

6. The walls thus derived were especially effective for the removal by oxidation of soils splattered onto them during the cooking of meats or other edible baked goods. Furthermore, when this same type sheet was applied to the bottom of the oven, very rapid cleanup of even heavy spills was obtained at normal cooking temperatures.

Instead of the sodium silicate being used as the adhesive, ethyl silicate, guanidine silicate, potassium silicate, colloidal silica, colloidal alumina or other adhesive could be used to give equally good adhesion and oxidation characteristics for the catalytic coating.

The same type catalytic sheeting was applied to the exit duct from a paint spraying chamber and enamel baking facility. The volatile products from the paint and enamel finishing were oxidized and essentially completely removed as the effluent passed through the discharge duct lined with the catalytic coating.

When the oven walls in the industrial baking oven were also lined with the catalytic sheeting, spattered paint and enamel as well as the volatile combustible components were oxidized so that only an ash residue remained on the catalytic walls.

Instead of the silica fibers specified in Item 1 above, there can be used asbestos fibers, potassium titanate fibers, mullite fibers, glass fibers or even rock wool fibers.

What is claimed is:

1. An oven employed for heating, which during normal use will have oxidizable waste form upon its interior surfaces, said oven having a paper-like fibrous catalytic structure adapted to fit at least one of the interior surfaces of said oven, the paper-like, fibrous catalytic structure consisting essentially of a fibrous support material selected from the group consisting of glass wool, rock wool, fibrous ceramic alumina, quartz fibers, silica fibers, potassium titanate, refractory metallic filaments, zirconia fibers, sillimanite fibers, mullite fibers, or asbestos fibers, said support material being formed into a paper-like structure having distributed therein a catalytic material selected from the group consisting of (a) elemental ruthenium, rhodium, palladium, platinum, (b) the oxides, cerates, chromates, chromites, manganates, manganites, tungstates, molybdates, or vanadates of iron, cobalt, nickel, palladium, platinum, ruthenium, rhodium, manganese, chromium, copper, molybdenum, tungsten or the rare earths, and (c) mixtures thereof, the structure acting to remove said oxidizable waste by catalytic oxidation.

2. The apparatus of claim 1 wherein the oven is a food cooking oven.

3. The apparatus of claim 1 wherein the paper-like fibrous catalytic structure is attached to the interior surface of the oven with a fastening means.

4. The apparatus of claim 3 wherein the fastening means is an adhesive selected from the group consisting of sodium silicate, potassium silicate, lithium silicate,

have oxidizable waste form upon its floor, said oven having a paper-like fibrous catalytic structure placed on its floor, the paper-like fibrous catalytic structure consisting essentially of glass wool formed into a paperlike structure impregnated with the oxides of manganese, cobalt and cerium. 

2. The apparatus of claim 1 wherein the oven is a food cooking oven.
 3. The apparatus of claim 1 wherein the paper-like fibrous catalytic structure is attached to the interior surface of the oven with a fastening means.
 4. The apparatus of claim 3 wherein the fastening means is an adhesive selected from the group consisting of sodium silicate, potassium silicate, lithium silicate, ethyl silicate, guanidine silicate, colloidal silica, aluminum hydroxide gel and magnesium hydroxide gel.
 5. A food cooking oven, which during normal use will have oxidizable waste form upon its floor, said oven having a paper-like fibrous catalytic structure placed on its floor, the paper-like fibrous catalytic structure consisting essentially of glass wool formed into a paper-like structure impregnated with the oxides of manganese, cobalt and cerium. 